Liquid to air heat exchangers transfer heat between a liquid and air or another gas. For example, a heat exchanger may be configured to cool relatively warm air. As such, the heat exchanger may receive warm air along with a cool liquid. Heat from the air may be absorbed by the liquid so as to cool the air and heat the liquid. As such, cooler air may exit from the heat exchanger along with a warmer liquid following the heat exchange therebetween.
In order to exchange heat between an air and a liquid, a heat exchanger may include a plurality of first channels through which the liquid passes and a plurality of second channels through which the air flows. These channels may be mutually exclusive, but may be arranged and constructed so as to facilitate heat exchange between the air and the liquid passing through the respective channels. In this regard, the first and second channels through which the liquid and air flow, respectively, may be positioned in an alternating fashion such that a common wall separates a channel through which liquid passes from a channel through which air flows, thereby facilitating heat exchange between the liquid and the air. Additionally, the heat exchanger may include fins, such as fins extending from the walls that define the respective channels into, for example, the channels through which the air flows in order to facilitate heat exchange therebetween.
In some instances, the liquid that is provided to the heat exchanger has a temperature lower than the freezing temperature of water in order to provide for more effective heat transfer. In this instance, liquid that condenses from the warm, humid air that is received by the heat exchanger for cooling may freeze within the heat exchanger. Over the course of time, the build up of ice within the heat exchanger will limit the cooling capacity of the heat exchanger by limiting the amount of air that may flow through the heat exchanger. Eventually, sufficient amounts of ice may form within the heat exchanger so as to prevent air from flowing through the heat exchanger, thereby eliminating further heat exchange.
In order to avoid the limitations upon the cooling capacity occasioned by freezing within the heat exchanger, the system may be designed such that the liquid provided to the heat exchanger has a temperature above the freezing temperature of water. For example, the heat exchanger may be positioned at the end of a cooling circuit so that the liquid provided to the heat exchanger is above the freezing temperature of water. However, this technique generally requires additional plumbing and more complex controls and sensors, thereby disadvantageously increasing the weight of the system. In instances in which the heat exchanger is employed in weight-sensitive application, such as applications carried vehicles, such as air vehicles, the increase in weight may, in turn, disadvantageously affect the performance of the vehicle. Additionally, the cooling capacity of the heat exchanger is disadvantageously limited by requiring the liquid to remain above the freezing temperature of water. Further, the use of liquid having a temperature above the freezing temperature of water will generally disadvantageously increase the air temperature at the exit of the heat exchanger, thereby potentially decreasing overall system performance.
Alternatively, the heat exchanger may be periodically taken out of service and defrosted. In this regard, the heat exchanger may be taken out of service by halting the flow of cool liquid to the heat exchanger. By continuing to provide warm air to the heat exchanger, the heat exchanger may be defrosted. By taking the heat exchanger out of service, however, the heat exchanger is unable to perform its function, thereby reducing quantity of air that is cooled and preventing continuous operation.